The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The HDA includes at least one disk, a spindle motor for rotating the disk, and a head stack assembly (HSA). The PCBA includes a disk controller for generating servo control signals. The HSA includes a head for reading and writing data from and to the disk. The HSA is controllably positioned in response to the generated servo control signals from the disk controller to move the head relative to tracks of the disk.
The HSA includes an actuator, at least one head gimbal assembly (HGA), and a flex cable assembly. The actuator includes an actuator body with one or more actuator arms extending from the actuator body. Each actuator arm supports the HGA that includes a head. An actuator coil is supported by the actuator body. The actuator coil interacts with a magnet to form a voice coil motor. The PCBA controls current passing through the actuator coil that results in a torque being applied to the actuator. The HSA further includes the flex cable assembly in electrical communication with the PCBA. The flex cable assembly supplies current to the coil and carries signals between the head and the PCBA.
Each HGA is attached to a distal end of one of the actuator arms and includes a suspension assembly that supports a head. The suspension assembly includes a base plate that is swage attached to the distal end of the actuator arm. The suspension assembly further includes a load beam and a pair of hinge arms that are each disposed between the swage plate and the load beam. The hinge arms are attached to the load beam with the load beam extending distally from the hinge arms and the actuator arm. The hinge arms allow the load beam to move the attached head relative to the actuator arm.
Disk flutter refers to one or more disk modes of vibration, wherein as the disk vibrates, at least a portion of the disk moves up and down (i.e., along the disk axis of rotation). Disk flutter is one of the known causes of mis-registration between the head and information tracks on the disk surface, known as “track mis-registration” or “TMR.”
An approach to compensate for disk flutter induced TMR is to change the design of the suspension assembly so as to vertically offset one of the hinge arms through the use of two small spacers. One of the spacers is inserted between the load beam and the hinge arm, and the other one of the spacers is inserted between the base plate and the hinge arm. Such a hinge offset can introduce a radial component to otherwise vertical head motion, the radial component being intended to at least partially cancel TMR. While such spacer offset approach can be effective in at least partially compensating for disk flutter induced off-track motion, this approach also introduces two additional spacers and increased assembly complexity. Therefore, there is a need in the art to find a way to reduce an increase in off-track motion due to disk flutter, while avoiding an increase in components and/or manufacturing complexity in comparison to the prior art.